Dual-band array antenna

ABSTRACT

A unitary antenna comprising two different arrays. The first is a group of waveguide antenna elements in alternately displaced rows forming a triangular grid structure and the second is another group of waveguide antenna elements forming a triangular grid structure within the first grid structure. The two groups of elements are dielectrically loaded, are polarized to radiate orthogonally to each other, and are designed to radiate at different frquency bands.

United States Patent [191 Harper et a1.

[ DUAL-BAND ARRAY ANTENNA [75] Inventors: W. Harold Harper, Oxon Hill;

William L. Thrift, Waldorf; Robert E. Hailey, Jr., Forestville, all of Md.

[73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

[22] Filed: July 21, 1972 [21] App]. No.: 273,915

US. Cl. 343/776, 343/777 Int. Cl. HOlq 13/00 Field of Search 343/725, 729, 754, 343/776, 777

[56] References Cited UNITED STATES PATENTS 3,706,998 12/1972 Hatchet 343/754 [m mmmm@ mama 14 wwm wm 22 mmm mm [451 Sept. 25, 1973 3,623,111 11/1971 Provencher 343/727 Primary ExaminerEli Lieberman Att0rneyR. S. Sciascia et a1.

5 Claims, 2 Drawing Figures m m w w m w 5132-? w LKBA'ND w w m w %i- (O.476Xl SBAND m w w @5 II DUAL-BAND ARRAY ANTENNA STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for The Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to array antennas and especially to array antennas which can be used effectively on more than one frequency band.

Modern ships of the US. fleet are loaded down with radar equipment which operates at various frequency bands in the microwave spectrum. Each radar set has its own antenna which takes up space on the masts. It would obviously be advantageous if a single antenna could be utilized for more than one set and more than one frequency band, since the number of antennas could then be reduced. Another advantage is that large apertures can be used at all the frequencies even on small ships.

BRIEF SUMMARY OF THE INVENTION The objects and advantages of the present invention are accomplished by interleaving two arrays of waveguide antenna elements, the elements being dielectrically loaded and each array being polarized orthogonally to the other so that each array is effectively isolated from the radiation of the other.

An object of this invention is to provide a dual-band, unitary, radar array antenna.

Other objects, advantages and novel features of the invention will become apparent from the follwong detailed description of the invention when considered in conjunction with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE FIGURE FIG. 1 is a schematic illustration of an embodiment of the invention; and

FIG. 2 is a diagram illustrating typical end dimensions for the waveguide antenna elements.

DETAILED DESCRIPTION The range of frequencies used at S-band is centered at a frequency nominally three times that of the L-band center frequency. Thus nine S-band radiators are to be placed in the same space as a single L-band radiator. In the design of the aperture of the dual-band array, the element spacings for both frequency bands have been chosen such that no grating lobes are formed in visible space (for normal shipboard coverage).

The spacing of the radiating elements in a planar array is constrained by the required scanning coverage of the array. For both arrays of the dual-band aperture to be completely filled, it is necessary to move the higher-frequency elements apart and to make them as small as practical. This makes area available for the lower frequency elements. The maximum element spacing without grating lobes in visible space is achievable with a triangular grid configuration. The element spacings are given by sin 1 sin \[1 i1; maximum azimuth scan angle,

-r tilt angle of the array,

E maximum positive elevation angle,

d, horizontal element spacing,

d,,= vertical element spacing.

It is assumed that each of four shipboard arrays would cover i50 in azimuth (normal shipboard coverage) to allow overlap between arrays. Furthermore the array face would be tilted back about 15 to allow coverage at high elevation angles. Using these coverage angles cil1=50, E,,=, and -r=l5) in Eqs. (1) and (2), it is found that d =O.627A and d,,=0.509A, which are the maximum element spacings. Element spacings less than 0.627A and/or 0509A may be chosen and no grating lobe peaks will enter visible space for the given scan coverage. If a 1],, less than (1509A is chosen, the d, calculated by Eq. (2) will be greater then 0627A, but the grating-lobe criterion still holds because d is a function of d Open-ended waveguides have advantages as radiating elements for both: bands: there is no problem of shading of one set of radiators by the other, radiators of both bands may be dielectrically loaded to reduce their size, and the radiators can be oriented to radiate orthogonal polarization and thus enhance the isolation between frequency bands.

The preceding considerations have led to the dualband grid configuration shown in FIG. 1. Both the S- band and L-band radiators l0 and 12, respectively, are dielectrically loaded (i.e., the interior of each waveguide is filled with dielectric material) to reduce their size. In addition the L-band radiators are double ridged. The S-band radiators are formed by loading standard C-band waveguide with a material 14 having a dielectric constant e-4.0. The L-band elements are loaded with the same =4.0) material and positioned so as to radiate orthogonally to the S-band elements. Furthermore, the element spacings, d -=0.635)t and d,,=0.476)\, satisfy Eqs. (1) and (2) such that scan coverage of a quadrant of a hemisphere can be achieved without grating lobes.

It can be seen that the elements of the array are in a triangular grid configuration if attention is focused on the typical S-band elements ll, l3, 15, for example.

The interleaved L-band elements 12 are also arranged in a triangular grid configuration, alternate rows being displaced to the right or the left. Each L-band element extends from an S-band element in one row to an S-band element in a row twice removed from it; thus, counting the topmost row of S-band elements in FIG. 1 as row 1, the L-band elements extend from the bottom of row 1 to the top of row 3. The L-band elements are also I-shaped to fit between the S-band elements in row 2.

The triangular grid arrangement permits the same space coverage with fewer array elements than a rectangular grid arrangement.

The element spacings of FIG. 1 were chosen to insure that no grating lobes exist in visible space at the center frequencies. At the upper end of an 8 percent band (1.3 or 3.9 GHz) a grating lobe just enters visible space. Even though the grating lobe enters visible space at these frequencies, the element pattern will probably not be broad enough to allow the grating lobe to have an appreciable amplitude.

Some of typical dimensions that may be employed are indicated in FIGS. 1 and 2. The array may, for example, consist of nine L-band and 110 S-band radiators l2 and 10, respectively. The physical center 22 of the array is marked by a circled cross. The L-band elements are physically longer than the S-band elements to allow a sidewall coax-to-waveguide transition. The dielectric material used to load the waveguides has a styrene base and a dielectric constant of 4.0.

The array is scanned electronically; the necessary scanning equipment is well-known and therefore will not be described herein.

Isolation between frequency bands is provided by utilizing orthogonal polarization for the radiation of the two groups of elements. Interaction between the two groups of elements is quite low so that either timesharing or simultaneous operation is possible.

In FIG. 2, one of the S-band elements 10 and one of the L-band elements are shown and typical dimensions for the loaded elements are shown. The loading, of course, allows the dimensions of the elements to be less than those of elements which are unloaded. This provides a saving in space.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of the United States ls:

1. An array antenna comprising, in combination:

a plurality of first rectangular antenna elements de signed to radiate efficiently at a first predetermined frequency band, said elements being arranged in rows wherein alternate rows are displaced laterally from each other so that a triangular grid structure is formed; and

a plurality of second antenna elements designed to radiate efficiently at a second predetermined frequency band which is different from the first, said elements being arranged in rows and alternate rows being displaced from each other so that a triangular grid structure is formed, wherein each second element extends between a first element in one row and a first element in a row twice removed from said one row,

said group of second antenna elements being interleaved among said elements of the first group,

the radiation from said first group of antenna elements being polarized orthogonally with respect to the radiation from said second group of antenna elements.

2. An array antenna as in claim I, wherein said antenna elements are formed from waveguide sections, all said antenna waveguide elements being dielectrically loaded by dielectric material which is placed within each waveguide element.

3. An array antenna as in claim 1, wherein both groups of antenna elements are symmetrical with respect to the center of said array antenna.

4. An array antenna as in claim 1, wherein the spacing of the antenna elements is such that no grating lobes are formed in visible space.

5. An array antenna as in claim 1, wherein each second antenna element is I-shaped. 

1. An array antenna comprising, in combination: a plurality of first rectangular antenna elements designed to radiate efficiently at a first predetermined frequency band, said elements being arranged in rows wherein alternate rows are displaced laterally from each other so that a triangular grid structure is formed; and a plurality of second antenna elements designed to radiate efficiently at a second predetermined frequency band which is different from the first, said elements being arranged in rows and alternate rows being displaced from each other so that a triangular grid structure is formed, wherein each second element extends between a first element in one row and a first element in a row twice removed from said one row, said group of second antenna elements being interleaved among said elements of the first group, the radiation from said first group of antenna elements being polarized orthogonally with respect to the radiation from said second group of antenna elements.
 2. An array antenna as in claim 1, wherein said antenna elements are formed from waveguide sections, all said antenna waveguide elements being dielectrically loaded by dielectric material which is placed within each waveguide element.
 3. An array antenna as in claim 1, wherein both groups of antenna elements are symmetrical with respect to the center of said array antenna.
 4. An array antenna as in claim 1, wherein the spacing of the antenna elements is such that no grating lobes are formed in visible space.
 5. An array antenna as in claim 1, wherein each second antenna element is I-shaped. 